He said that in the year before the ban came into force on 26 May 2016, Addiction Helper received 2,151 calls about spice.

That total has now been overtaken with one month to spare. Addiction Helper has received 2,464 spice-related calls in the 11 months since the ban was introduced under the Psychoactive Substances Act.

“The ban hasn’t made a blind bit of difference,” said Mr Gerrard. “More and more people are using this stuff.”

Mr Gerrard released the statistics to The Independent two weeks after it was reported that some town and city centres are facing what has been called a “zombie plague” of spice users.

Tony Lloyd, the crime commissioner for Manchester, one of the worst affected cities, said that since the ban, it had become far harder for police to stop the sale of potentially deadly strains of spice – instead of simply talking to head shop owners, they had to tackle criminal drug dealers.

City centre inspector Phil Spurgeon told the Manchester Evening News: “The reality with the Psychoactive Substances Act is that it has shifted supply onto the streets.

“The product was probably more consistent in the head shops. Now it’s more varied, the make-up is constantly changing. That’s why we’re seeing people collapsing, as the drug becomes more potent.”

This seemed to echo what critics had predicted before the ban was introduced, that the former legal highs trade would just go underground, passing from head shops into the hands of unscrupulous criminal street dealers with no interest in the safety of what they were selling.

The Independent has also learned that since the ban, spice and other former legal highs have actually become easier to obtain in some parts of the UK. In Bradford, West Yorkshire, one user said spice could now be ordered “like a takeaway”.

In London, there have been fears that addiction is being fuelled by pushers offering the homeless cut-price deals where instead of selling by weight, they dished out spice according to whatever money was in a rough sleeper’s pockets.

The ban on legal highs had – outside of prisons – only criminalised suppliers, but in December the Government made spice a Class B drug, meaning possession now carries a maximum penalty of five years in jail.

Mr Gerrard said there had been an immediate impact on the numbers of people calling Addiction Helper seeking assistance for themselves or a relative who was hooked on spice.

Between January and March this year, he added, there had been 20 per cent more calls about spice than in the same three months of last year.

“The reality is,” he said, “If you want drugs you will find them. Legal highs are so cheap that in a decade, they will probably outweigh [the problems of] all other drugs put together.”

Mr Gerrard stressed that he supported the ban on legal highs because he believed that outlawing the head shop trade had potentially prevented an even worse spice epidemic.

He added that although the aim should be to treat addicts, not punish and imprison them, making spice a Class A drug might act as a powerful deterrent to stop young people experimenting: “By making it only Class B or C you are almost saying ‘It’s not that bad’.”

He said, however, that the implementation of the ban on legal highs had been flawed because it had not been accompanied by proper Government funding for local authority prevention and addiction treatment services.

“It’s austerity,” he said. “The Government is failing people with any kind of addiction. They have cut services left, right and centre.”

The Home Office was unable to comment because of election purdah rules, but earlier this month Sarah Newton, the Minister for Vulnerability, Safeguarding and Countering Extremism, said: “Drugs can devastate lives and communities; we will not tolerate them. That is why last year we passed the Psychoactive Substances Act to outlaw so-called legal highs and introduced even tougher controls for synthetic cannabinoids, such as those found in spice.

“Our drug strategy, to be published shortly, will build on the work already undertaken to prevent drug use in our communities and help dependent individuals, including homeless people and those in prisons.”